INTRODUCTION

Topically applied drug products fall into two general categories: those applied to achieve local action and those applied to achieve systemic effects after absorption through the skin into the blood circulation. Local action can occur at or on the surface of the application site (e.g., stratum corneum); in the underlying tissues (e.g., epidermis and/or dermis); and in subcutaneous tissues (e.g., muscle or joint). Topically applied drug products include, but are not limited to, creams, gels, ointments, pastes, suspensions, lotions, foams, sprays, aerosols, solutions, and transdermal delivery systems (TDS). The definitions and descriptions of these dosage forms, as well as brief information on their composition and/or manufacturing processes, can be found in Pharmaceutical Dosage Forms 〈1151〉.